1. Field of the Invention
The present invention relates to an initial program loading (IPL) operation in a processor system.
2. Related Background Art
FIG. 4 is a block diagram showing the configuration of a conventional processor system in which IPL operation is performed. FIG. 5 is a flowchart of the basis operation of the conventional system in an IPL operation mode and in a normal start mode.
In the system shown in FIG. 4, the IPL operation mode is selected by an operation mode selection switch 43 (step S501), and a central processing unit (CPU) 40 starts operating (step S502). The CPU 40 then loads an initial program loader (hereinafter referred to simply as “initial program” or “IPL program”) held in a read-only memory (ROM) 41 added as an IPL storage to the processor system, and starts the initial program (step S503).
The CPU 40 initializes a communication portion 45 (sets communication conditions) by the started initial program (step S504), and downloads a system program from the outside of the processor system through a communication port 46. Writing of the downloaded system program to a random access memory (RAM) 42 or the like connected to the system is continued until the communication is finished (steps S505, S506). When the communication is finished, the downloaded system program is started (step S507). On the other hand, when a normal start mode is selected by the operation mode selection switch 43, the CPU starts operating in the normal mode and performs the normal operation (steps S508, S509).
As described above, for conventional processor systems, a method is generally used in which an initial program is provided in advance by being written into the ROM 41 or the like added to the processor system, and the initial program is loaded from the ROM 41 or the like added to the processor system when the IPL operation mode is selected.
In the conventional system, however, it is difficult to rewrite the IPL program if the IPL program is provided by being written into a non-rewritable. To rewrite IPL program, it is necessary to change the ROM or to use an erasing and writing device specially provided for the ROM.
Further, having an IPL-storage ROM necessitates a special circuit for access the ROM, and different erasing and writing methods are required with respect to different ROM manufacturers or various types of IPL-storage ROM. To enable interchange or replacement of ROMs, therefore, it is necessary to select the circuit configuration and the control method suitable for ROMs to be used.